[v1.0.5] crop disease reduction bugged?

After reading the wiki (Farming - Farthest Frontier) I think I might experience a bug regarding crop disease reduction, but I’m not sure if my understanding of the wiki is correct and hence ask for clarification.

I have a field with an intra-year rotation of turnip-buckwheat-turnip (starting in April) showing a Clubroot infection of 26% (10+16) by November. The early turnips had a 10% infection (possibly from spread) which, according to the wiki, should have been mitigated by 5% by the unaffected buckwheat planting in between, but was not. This seems like a bug if my understanding of the wiki is right - is it?

I’m also not sure if the April turnips could have originated the Clubroot infection themselves (despite the 10-day planting process not falling into the active period of the Clubroot disease [June-September]) or if spread from another field during June is the only possible infection origin as per intended mechanic.

The wiki states that

“Diseases spontaneously appear in a field whenever a crop is planted, each particular disease that a crop is susceptible for is rolled for. … each time a crop is planted (including clover), the magnitude of every disease already present changes: it goes up if the new crop is susceptible to it, and it goes down if it is not…”

Does this mean that the rolling for originating (as in - not getting it via spread) a disease (Infection Chance) in a certain planting happens only once (at the beginning or end of the 10 day planting window?) and not monthly like the spread chance does? So I’m unsure if “a crop is planted” refers to the initial planting process itself as a one-time event or to the crop existing in the field after being planted.

Hope somebody in the know can clarify the wording here, so we can identify possible bugs as such. Thanks!